This invention relates to wireless data communication technology and in particular to data communication technology which facilitates the location of items within an area having wireless data communications.
Currently known wireless data communication systems include the Bluetooth system, the specification for which is available at www.bluetooth.com. The Bluetooth communication specification provides for wireless data communication links between a master device and a plurality of slave devices within a piconet comprising an area within a range of approximately 10 meters from the master device. Adjacent piconets can conduct relay communications between their respective masters and thereby form larger networks called scatternets. Bluetooth masters coordinate the traffic within and between piconets. Masters can be positioned in a cellular manner as illustrated in FIG. 1 to provide wireless communications within an area, such as an industrial, educational, or health care facility. Because Bluetooth slave devices associate with the master units, it is possible to determine the location of a slave unit within a particular piconet of the system by reason of the association, and thereby locate the unit within a range of approximately 10 meters. In connection with operation of a scatternet, the Bluetooth master devices may relay the identity of mobile slave devices that are within their individual piconets to a host processor for purposes of tracking the location of a mobile slave device, or the location of a person carrying a device.
In some cases it is desirable to determine the location of a device which is not a slave unit. One technique for locating devices is to provide such devices with active or passive back scatter RFID tags. An RFID reader can be placed at a selected location and can be used to determine the range from the known location of the RFID reader to an RFID tag on a device within a zone covered by the RFID reader.
It is an object of the present invention to provide an improved method and system for locating objects having either a data communications mobile unit or an RFID tag.
In accordance with the invention there is provided a method for locating items. A plurality of fixed devices are distributed over an area containing the items. The fixed devices are operated as master units using a first wireless data communications protocol, wherein each of the master units controls slave units within an area corresponding to the location of each of the fixed devices. The operating includes identifying the slave units thereby to locate items corresponding to the slave units within the area corresponding to the location of each fixed device. The fixed devices are further operated as RFID readers to identify and locate items having RFID tags with respect to the fixed device.
In a preferred embodiment of the method, items may be provided with both slave units using the wireless data communications protocol and with RFID tags. The fixed devices may be operable as a master unit and as an RFID reader during alternating time periods. A plurality of the fixed devices are preferably distributed at distances corresponding to twice the range of the devices when operated as RFID readers. The operation to identify and locate items having RFID tags may preferably comprise transmitting RFID reader signals, receiving RFID response signals and determining the range of an RFID device from the fixed device using the response signals. In a particularly preferred embodiment, range may be determined from the phase of the response signals and the phase may be determined at a plurality of frequencies to resolve phase ambiguities. The device may transmit and receive RFID signals on directional antenna beams to additionally determine the direction of an RFID device with respect to a fixed device.
In accordance with the invention there is provided a system for locating items which includes a plurality of fixed devices distributed over an area containing the items and sub-dividing the area into a plurality of cells. Each fixed device corresponds to one of more of the cells. The fixed devices each comprise a transmitter, a receiver and a signal processor. Each fixed device is arranged to operate as master unit using a first wireless data communications protocol to communicate with slave units in the one or more cells corresponding to the fixed device to thereby locate items having the slave devices in the one or more cells. The fixed device is further arranged to operate as an RFID tag reader to identify and locate RFID tags on items in the one or more cells.
In a preferred arrangement the fixed devices are arranged to communicate location data relating to the items having slave units and the items having RFID tags to a host processor.
In accordance with the invention there is provided a device having at least one transmitter and at least one receiver. The device further includes a processor coupled to provide signals for transmission by the transmitter and to process signals received by the receiver. The processor includes a first program for sending and receiving digital data signals using a first wireless data communication protocol and thereby identifying remote units within range for communications therewith. The processor further includes a second program for sending and receiving RFID reading signals to thereby identify RFID tags within range for identification.
In a preferred arrangement, the second program further provides for determining range from the RFID tags to the device. The device may include two transmitters and two receivers for respectively transmitting and receiving wireless data communications signals and RFID reading signals. The two transmitters and two receivers are preferably coupled to the processor by a common baseband signal processor. The processor may be arranged to cause the device to operate using the first and second programs during alternate time intervals. The processor may be further programmed to provide data identifying the remote units within range and data identifying the RFID tags within range to a host processor.
For a better understanding of the present invention, together with other and further objects, reference is made to the following description taken in conjunction with the accompanying drawings, and its scope will be pointed out in the appended claims.